Provided is a pressure sensor, comprising a housing with a pressure port, which projects into the housing, and which is fitted with a micromechanical pressure sensing element, which is arranged in the housing. The pressure sensing element is connected to the pressure port in such a manner that it seals a passage of the pressure port, by way of which a pressure acts directly on the pressure sensing element. In addition, a method for manufacturing such a pressure sensor is provided.
Such pressure sensors are used for monitoring the pressure of the pressure fluctuations in various fields of applications exhibiting widely varying pressure ranges. For example, in control units for piston motors or in piston compressors the requirements with respect to pressure stability, temperature range and service life are very stringent. In particular, under very high and to some extent vigorous pressure fluctuations and maximum pressures, which may occur, the reliability of the pressure-loaded connections, which are often designed as a cemented joint, must be guaranteed under all operating conditions.
A typical design of a pressure sensor is described, for example, in the DE 102 60 105 A1. However, in this case the description does not refer to a surrounding housing. A pressure sensing element is mounted with its diaphragm over the passage of a pressure port through intercalation of a glass base, so that a pressure, which is applied in the passage of the pressure port and that is to be measured, acts on the diaphragm. Measurement resistors are arranged on the opposite side of the diaphragm (this side is often called, as also below, the front side of the pressure sensing element). These measurement resistors determine by means of their resistance variation the applied pressure or a pressure fluctuation. The variation in resistance results, as well-known, from a deflection of the diaphragm from its quiescent position as a consequence of a change in the applied pressure and the associated tensile load or pressure load on the diaphragm. When pressure is applied, the connection of the pressure sensing element on the pressure port and optionally also the connections between two others of the components—pressure sensing element, base, pressure port, and housing—are under high tension. This leads, especially at high pressure and long term usage of the pressure sensor, to reliability problems. A comparable pressure sensor is also described in the U.S. Pat. No. 7,024,937.
These problems increase with the statutory requirement stipulating the use of lead free materials, since it is possible only with difficulty to produce in terms of pressure and temperature a reliable cemented joint between the lead free components of a pressure sensor, as described, for example, in the EP 1 785 710 A2, or to produce reliable cemented joints, which are made of other materials that are capable of withstanding higher chemical and mechanical stresses, over the entire area of application.
Therefore, the object of the invention is to provide a pressure sensor that satisfies the requirements of reliability even at high pressures and pressure differentials while simultaneously using lead free materials.